1. Field of the Invention
The present invention relates to devices for transmitting digital data, and more specifically to transmission of digital information on a two-way conductor.
2. Description of Related Art
There are several conventional two-way transmission busses that use one or more two-way conductors for transmitting digital data. For example, the I2C bus devised by Philips is commonly used in audio and video applications. The I2C bus has one-way supply lines in the form of a supply line for the positive supply voltage (e.g., 5 volts) and a supply line for ground. Additionally, the I2C bus has a clock line for transmitting a clock signal that can be a one-way signal or a two-way signal (e.g., when there are several master units on the bus), and a two-way data line for the digital data to be transmitted. When data is not being transmitted, the data line is pulled to a positive potential by a pulling device consisting of a resistor. To transmit on the two-way data line, a master or slave circuit takes over the data line and imposes negative pulses corresponding to the sequence of 1's and 0's of the information to be transmitted (i.e., addresses and data) at the clock rate in accordance with a specified protocol.
When making an electronic system for an application, the various electronic circuits required for the different functions of the system are chosen from the catalogs of suppliers of electronic circuits. Depending on the functions being sought (e.g., depending on if what is being sought is a microprocessor, an audio amplifier or tuner, a static or dynamic memory, and/or a non-volatile or other type of memory), the technologies of the electronic circuits that are available are not always equivalent. For example, there is a current trend towards the development of technologies and circuit structures capable of operating at low supply voltages (e.g., 2.5 volts or less). However, while microprocessors and memories that operate at 2.5 volts are currently available, other electronic circuits that require a great deal of power (e.g., tuners) are currently only available for operation at 5 volts. If it is desired to use circuits operating at different voltages in the same electronic system, it is necessary to provide for the matching of the levels of the data to be transmitted.
Furthermore, certain electronic circuits (e.g., amplifiers) are highly sensitive to noise. In a system having many electronic circuits that communicate through the same transmission bus, a sensitive circuit (such as the tuner) can be significantly disturbed by all of the information transmitted on the bus that is intended for other circuits.